Networks are everywhere, including biological, traffic, communication and social networks [1]}, [2]}, [3]}. In recent years, the study of social networks have received increasing levels of attention [4]}. Social network analysis uses graph theory to analyse social structure and relations among people and among groups in organisations [5]}. Important data or information can be obtained through social network analysis. Such data are often useful in fields such as marketing, economics and industrial engineering [6]}.
